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<a href="asio__local__stream__socket_8cpp.html">Go to the documentation of this file.</a><div class="fragment"><div class="line"><a id="l00001" name="l00001"></a><span class="lineno">    1</span><span class="comment">/* Flow-IPC: Core</span></div>
<div class="line"><a id="l00002" name="l00002"></a><span class="lineno">    2</span><span class="comment"> * Copyright 2023 Akamai Technologies, Inc.</span></div>
<div class="line"><a id="l00003" name="l00003"></a><span class="lineno">    3</span><span class="comment"> *</span></div>
<div class="line"><a id="l00004" name="l00004"></a><span class="lineno">    4</span><span class="comment"> * Licensed under the Apache License, Version 2.0 (the</span></div>
<div class="line"><a id="l00005" name="l00005"></a><span class="lineno">    5</span><span class="comment"> * &quot;License&quot;); you may not use this file except in</span></div>
<div class="line"><a id="l00006" name="l00006"></a><span class="lineno">    6</span><span class="comment"> * compliance with the License.  You may obtain a copy</span></div>
<div class="line"><a id="l00007" name="l00007"></a><span class="lineno">    7</span><span class="comment"> * of the License at</span></div>
<div class="line"><a id="l00008" name="l00008"></a><span class="lineno">    8</span><span class="comment"> *</span></div>
<div class="line"><a id="l00009" name="l00009"></a><span class="lineno">    9</span><span class="comment"> *   https://www.apache.org/licenses/LICENSE-2.0</span></div>
<div class="line"><a id="l00010" name="l00010"></a><span class="lineno">   10</span><span class="comment"> *</span></div>
<div class="line"><a id="l00011" name="l00011"></a><span class="lineno">   11</span><span class="comment"> * Unless required by applicable law or agreed to in</span></div>
<div class="line"><a id="l00012" name="l00012"></a><span class="lineno">   12</span><span class="comment"> * writing, software distributed under the License is</span></div>
<div class="line"><a id="l00013" name="l00013"></a><span class="lineno">   13</span><span class="comment"> * distributed on an &quot;AS IS&quot; BASIS, WITHOUT WARRANTIES OR</span></div>
<div class="line"><a id="l00014" name="l00014"></a><span class="lineno">   14</span><span class="comment"> * CONDITIONS OF ANY KIND, either express or implied.</span></div>
<div class="line"><a id="l00015" name="l00015"></a><span class="lineno">   15</span><span class="comment"> * See the License for the specific language governing</span></div>
<div class="line"><a id="l00016" name="l00016"></a><span class="lineno">   16</span><span class="comment"> * permissions and limitations under the License. */</span></div>
<div class="line"><a id="l00017" name="l00017"></a><span class="lineno">   17</span><span class="comment"></span> </div>
<div class="line"><a id="l00018" name="l00018"></a><span class="lineno">   18</span><span class="comment">/// @file</span></div>
<div class="line"><a id="l00019" name="l00019"></a><span class="lineno">   19</span><span class="comment"></span><span class="preprocessor">#include &quot;<a class="code" href="asio__local__stream__socket_8hpp.html">ipc/transport/asio_local_stream_socket.hpp</a>&quot;</span></div>
<div class="line"><a id="l00020" name="l00020"></a><span class="lineno">   20</span><span class="preprocessor">#include &quot;<a class="code" href="ipc__core_2src_2ipc_2transport_2error_8hpp.html">ipc/transport/error.hpp</a>&quot;</span></div>
<div class="line"><a id="l00021" name="l00021"></a><span class="lineno">   21</span><span class="preprocessor">#include &lt;flow/common.hpp&gt;</span></div>
<div class="line"><a id="l00022" name="l00022"></a><span class="lineno">   22</span><span class="preprocessor">#include &lt;boost/array.hpp&gt;</span></div>
<div class="line"><a id="l00023" name="l00023"></a><span class="lineno">   23</span> </div>
<div class="line"><a id="l00024" name="l00024"></a><span class="lineno">   24</span><span class="preprocessor">#ifndef FLOW_OS_LINUX </span><span class="comment">// Sanity-re-check.  We&#39;ll be sending sockets through sockets, etc., which requires Linux.</span></div>
<div class="line"><a id="l00025" name="l00025"></a><span class="lineno">   25</span><span class="keyword">static_assert</span>(<span class="keyword">false</span>, <span class="stringliteral">&quot;Should not have gotten to this line; should have required Linux; this .cpp file assumes it.  &quot;</span></div>
<div class="line"><a id="l00026" name="l00026"></a><span class="lineno">   26</span>                       <span class="stringliteral">&quot;Might work in other POSIX OS (e.g., macOS) but must be checked/tested.&quot;</span>);</div>
<div class="line"><a id="l00027" name="l00027"></a><span class="lineno">   27</span><span class="preprocessor">#endif</span></div>
<div class="line"><a id="l00028" name="l00028"></a><span class="lineno">   28</span><span class="preprocessor">#include &lt;sys/types.h&gt;</span></div>
<div class="line"><a id="l00029" name="l00029"></a><span class="lineno">   29</span><span class="preprocessor">#include &lt;sys/socket.h&gt;</span></div>
<div class="line"><a id="l00030" name="l00030"></a><span class="lineno">   30</span> </div>
<div class="line"><a id="l00031" name="l00031"></a><span class="lineno"><a class="line" href="namespaceipc_1_1transport.html">   31</a></span><span class="keyword">namespace </span><a class="code hl_namespace" href="namespaceipc_1_1transport_1_1asio__local__stream__socket.html">ipc::transport::asio_local_stream_socket</a></div>
<div class="line"><a id="l00032" name="l00032"></a><span class="lineno">   32</span>{</div>
<div class="line"><a id="l00033" name="l00033"></a><span class="lineno">   33</span> </div>
<div class="line"><a id="l00034" name="l00034"></a><span class="lineno">   34</span><span class="comment">// Free function implementations.</span></div>
<div class="line"><a id="l00035" name="l00035"></a><span class="lineno">   35</span> </div>
<div class="line"><a id="l00036" name="l00036"></a><span class="lineno"><a class="line" href="namespaceipc_1_1transport_1_1asio__local__stream__socket.html#a1022dfd42e9a0d6eab8384b0352decb0">   36</a></span><span class="keywordtype">size_t</span> <a class="code hl_function" href="namespaceipc_1_1transport_1_1asio__local__stream__socket.html#a1022dfd42e9a0d6eab8384b0352decb0">nb_write_some_with_native_handle</a>(flow::log::Logger* logger_ptr,</div>
<div class="line"><a id="l00037" name="l00037"></a><span class="lineno">   37</span>                                        <a class="code hl_typedef" href="namespaceipc_1_1transport_1_1asio__local__stream__socket.html#a1788f9dbd896bb71b3693f9ae25b40ae">Peer_socket</a>* peer_socket_ptr,</div>
<div class="line"><a id="l00038" name="l00038"></a><span class="lineno">   38</span>                                        <a class="code hl_struct" href="structipc_1_1util_1_1Native__handle.html">Native_handle</a> payload_hndl, <span class="keyword">const</span> <a class="code hl_typedef" href="namespaceipc_1_1util.html#ae0be7edba7e30ffa3f8b742af621f2ab">util::Blob_const</a>&amp; payload_blob,</div>
<div class="line"><a id="l00039" name="l00039"></a><span class="lineno">   39</span>                                        <a class="code hl_typedef" href="namespaceipc.html#aa3192e586cc45d3e7c22463bf2760f89">Error_code</a>* err_code)</div>
<div class="line"><a id="l00040" name="l00040"></a><span class="lineno">   40</span>{</div>
<div class="line"><a id="l00041" name="l00041"></a><span class="lineno">   41</span>  <span class="keyword">using </span>boost::system::system_category;</div>
<div class="line"><a id="l00042" name="l00042"></a><span class="lineno">   42</span>  <span class="keyword">using </span>boost::array;</div>
<div class="line"><a id="l00043" name="l00043"></a><span class="lineno">   43</span>  <span class="keyword">namespace </span>sys_err_codes = boost::system::errc;</div>
<div class="line"><a id="l00044" name="l00044"></a><span class="lineno">   44</span>  using ::sendmsg;</div>
<div class="line"><a id="l00045" name="l00045"></a><span class="lineno">   45</span>  using ::msghdr;</div>
<div class="line"><a id="l00046" name="l00046"></a><span class="lineno">   46</span>  using ::iovec;</div>
<div class="line"><a id="l00047" name="l00047"></a><span class="lineno">   47</span>  using ::cmsghdr;</div>
<div class="line"><a id="l00048" name="l00048"></a><span class="lineno">   48</span>  <span class="comment">// using ::SOL_SOCKET; // It&#39;s a macro apparently.</span></div>
<div class="line"><a id="l00049" name="l00049"></a><span class="lineno">   49</span>  using ::SCM_RIGHTS;</div>
<div class="line"><a id="l00050" name="l00050"></a><span class="lineno">   50</span>  using ::MSG_DONTWAIT;</div>
<div class="line"><a id="l00051" name="l00051"></a><span class="lineno">   51</span>  using ::MSG_NOSIGNAL;</div>
<div class="line"><a id="l00052" name="l00052"></a><span class="lineno">   52</span>  <span class="comment">// using ::errno; // It&#39;s a macro apparently.</span></div>
<div class="line"><a id="l00053" name="l00053"></a><span class="lineno">   53</span> </div>
<div class="line"><a id="l00054" name="l00054"></a><span class="lineno">   54</span>  FLOW_ERROR_EXEC_AND_THROW_ON_ERROR(<span class="keywordtype">size_t</span>, <a class="code hl_function" href="namespaceipc_1_1transport_1_1asio__local__stream__socket.html#a1022dfd42e9a0d6eab8384b0352decb0">nb_write_some_with_native_handle</a>,</div>
<div class="line"><a id="l00055" name="l00055"></a><span class="lineno">   55</span>                                     logger_ptr, peer_socket_ptr, payload_hndl, payload_blob, _1);</div>
<div class="line"><a id="l00056" name="l00056"></a><span class="lineno">   56</span>  <span class="comment">// ^-- Call ourselves and return if err_code is null.  If got to present line, err_code is not null.</span></div>
<div class="line"><a id="l00057" name="l00057"></a><span class="lineno">   57</span> </div>
<div class="line"><a id="l00058" name="l00058"></a><span class="lineno">   58</span>  <span class="comment">/* To reader/maintainer: The below isn&#39;t that difficult, but if you need exact understanding and definitely if you</span></div>
<div class="line"><a id="l00059" name="l00059"></a><span class="lineno">   59</span><span class="comment">   * plan to make changes -- even just clarifications or changes in the doc header -- then read the entire doc header</span></div>
<div class="line"><a id="l00060" name="l00060"></a><span class="lineno">   60</span><span class="comment">   * of nb_read_some_with_native_handle() first. */</span></div>
<div class="line"><a id="l00061" name="l00061"></a><span class="lineno">   61</span> </div>
<div class="line"><a id="l00062" name="l00062"></a><span class="lineno">   62</span>  assert(peer_socket_ptr);</div>
<div class="line"><a id="l00063" name="l00063"></a><span class="lineno">   63</span>  <span class="keyword">auto</span>&amp; peer_socket = *peer_socket_ptr;</div>
<div class="line"><a id="l00064" name="l00064"></a><span class="lineno">   64</span> </div>
<div class="line"><a id="l00065" name="l00065"></a><span class="lineno">   65</span>  FLOW_LOG_SET_CONTEXT(logger_ptr, Log_component::S_TRANSPORT);</div>
<div class="line"><a id="l00066" name="l00066"></a><span class="lineno">   66</span>  FLOW_LOG_TRACE(<span class="stringliteral">&quot;Connected local peer socket wants to write from location @ [&quot;</span> &lt;&lt; payload_blob.data() &lt;&lt; <span class="stringliteral">&quot;] &quot;</span></div>
<div class="line"><a id="l00067" name="l00067"></a><span class="lineno">   67</span>                 <span class="stringliteral">&quot;plus native handle [&quot;</span> &lt;&lt; payload_hndl &lt;&lt; <span class="stringliteral">&quot;].  Will try to send.&quot;</span>);</div>
<div class="line"><a id="l00068" name="l00068"></a><span class="lineno">   68</span> </div>
<div class="line"><a id="l00069" name="l00069"></a><span class="lineno">   69</span>  <span class="comment">/* Let us send as much as possible of payload_blob; and the native socket payload_hndl.</span></div>
<div class="line"><a id="l00070" name="l00070"></a><span class="lineno">   70</span><span class="comment">   * As explicitly documented in boost.asio docs: it does not provide an API for the latter (fairly hairy</span></div>
<div class="line"><a id="l00071" name="l00071"></a><span class="lineno">   71</span><span class="comment">   * and Linux-specific) feature, but it is doable by using sendmsg() natively via peer_socket.native_handle()</span></div>
<div class="line"><a id="l00072" name="l00072"></a><span class="lineno">   72</span><span class="comment">   * which gets the native handle (a/k/a FD).</span></div>
<div class="line"><a id="l00073" name="l00073"></a><span class="lineno">   73</span><span class="comment">   *</span></div>
<div class="line"><a id="l00074" name="l00074"></a><span class="lineno">   74</span><span class="comment">   * Side note: After I (ygoldfel) had written this and async_write_with_native_handle() (which calls us),</span></div>
<div class="line"><a id="l00075" name="l00075"></a><span class="lineno">   75</span><span class="comment">   * I found validation for the approach in boost.asio docs in their example for Peer_socket::native_non_blocking(),</span></div>
<div class="line"><a id="l00076" name="l00076"></a><span class="lineno">   76</span><span class="comment">   * which shows how to implement async_sendfile(), spiritually similar to our thing which is essentially</span></div>
<div class="line"><a id="l00077" name="l00077"></a><span class="lineno">   77</span><span class="comment">   * a case of an analogous hypothetical async_sendmsg().  Subtlety: we, too, could have used native_non_blocking(),</span></div>
<div class="line"><a id="l00078" name="l00078"></a><span class="lineno">   78</span><span class="comment">   * as their example does; and the only reason we did not is that `sendmsg()` happens to support a per-call flag</span></div>
<div class="line"><a id="l00079" name="l00079"></a><span class="lineno">   79</span><span class="comment">   * that forces a non-blocking transmission, so one needn&#39;t deal with socket state.  Subtlety: realize (as per</span></div>
<div class="line"><a id="l00080" name="l00080"></a><span class="lineno">   80</span><span class="comment">   * boost.asio docs) that Peer_socket::non_blocking() is orthogonal to this entirely; it is orthogonal to</span></div>
<div class="line"><a id="l00081" name="l00081"></a><span class="lineno">   81</span><span class="comment">   * native_non_blocking() and the per-call flag thing. */</span></div>
<div class="line"><a id="l00082" name="l00082"></a><span class="lineno">   82</span> </div>
<div class="line"><a id="l00083" name="l00083"></a><span class="lineno">   83</span>  iovec native_buf1 = { <span class="keyword">const_cast&lt;</span><span class="keywordtype">void</span>*<span class="keyword">&gt;</span>(payload_blob.data()), payload_blob.size() };</div>
<div class="line"><a id="l00084" name="l00084"></a><span class="lineno">   84</span>  <span class="comment">// (const_cast&lt;&gt; is OK, as sendmsg() is read-only. Probably the API is const-janky due to iovec&#39;s reuse in recvmsg().)</span></div>
<div class="line"><a id="l00085" name="l00085"></a><span class="lineno">   85</span> </div>
<div class="line"><a id="l00086" name="l00086"></a><span class="lineno">   86</span>  msghdr sendmsg_hdr =</div>
<div class="line"><a id="l00087" name="l00087"></a><span class="lineno">   87</span>  {</div>
<div class="line"><a id="l00088" name="l00088"></a><span class="lineno">   88</span>     0, <span class="comment">// msg_name - Address; not used; we are connected.</span></div>
<div class="line"><a id="l00089" name="l00089"></a><span class="lineno">   89</span>     0, <span class="comment">// msg_namelen - Ditto.</span></div>
<div class="line"><a id="l00090" name="l00090"></a><span class="lineno">   90</span>     <span class="comment">/* msg_iov - Scatter/gather array.  We just put the one blob here.  It&#39;s natural to instead put a</span></div>
<div class="line"><a id="l00091" name="l00091"></a><span class="lineno">   91</span><span class="comment">      * a buffer sequence, meaning N&gt;=1 buffers, here.  There&#39;s a to-do elsewhere as of this writing to</span></div>
<div class="line"><a id="l00092" name="l00092"></a><span class="lineno">   92</span><span class="comment">      * make that API as well; as of now it&#39;s not needed.  Take a look inside boost.asio for how they convert</span></div>
<div class="line"><a id="l00093" name="l00093"></a><span class="lineno">   93</span><span class="comment">      * between the 2; it&#39;s not rocket science, but we can either reuse their code or learn from it;</span></div>
<div class="line"><a id="l00094" name="l00094"></a><span class="lineno">   94</span><span class="comment">      * for example there&#39;s the matter of MAX_IOV (max size of this array). */</span></div>
<div class="line"><a id="l00095" name="l00095"></a><span class="lineno">   95</span>     &amp;native_buf1,</div>
<div class="line"><a id="l00096" name="l00096"></a><span class="lineno">   96</span>     1, <span class="comment">// msg_iovlen - # elements in msg_iov.</span></div>
<div class="line"><a id="l00097" name="l00097"></a><span class="lineno">   97</span> </div>
<div class="line"><a id="l00098" name="l00098"></a><span class="lineno">   98</span>     <span class="comment">/* The other 3 fields can be uninitialized: msg_flags is unused; msg_control[len] are set below.</span></div>
<div class="line"><a id="l00099" name="l00099"></a><span class="lineno">   99</span><span class="comment">      * The language won&#39;t let me leave them as garbage though so: */</span></div>
<div class="line"><a id="l00100" name="l00100"></a><span class="lineno">  100</span>     0, 0, 0</div>
<div class="line"><a id="l00101" name="l00101"></a><span class="lineno">  101</span>  };</div>
<div class="line"><a id="l00102" name="l00102"></a><span class="lineno">  102</span> </div>
<div class="line"><a id="l00103" name="l00103"></a><span class="lineno">  103</span>  <span class="comment">/* What&#39;s left is to set up msg_control[len] which is how we send the native handle (payload_hndl).</span></div>
<div class="line"><a id="l00104" name="l00104"></a><span class="lineno">  104</span><span class="comment">   * This is based on example snippet taken from Linux `man cmsg`.  FWIW it&#39;s rather difficult to figure out</span></div>
<div class="line"><a id="l00105" name="l00105"></a><span class="lineno">  105</span><span class="comment">   * how to write it from the rest of the documentation, which is likely complete and correct but opaque; the</span></div>
<div class="line"><a id="l00106" name="l00106"></a><span class="lineno">  106</span><span class="comment">   * example is invaluable.  Note we are particularly using the SOL_SOCKET/SCM_RIGHTS technique. */</span></div>
<div class="line"><a id="l00107" name="l00107"></a><span class="lineno">  107</span> </div>
<div class="line"><a id="l00108" name="l00108"></a><span class="lineno">  108</span>  <span class="keyword">constexpr</span> <span class="keywordtype">size_t</span> N_PAYLOAD_FDS = 1;</div>
<div class="line"><a id="l00109" name="l00109"></a><span class="lineno">  109</span>  <span class="keyword">union</span></div>
<div class="line"><a id="l00110" name="l00110"></a><span class="lineno">  110</span>  {</div>
<div class="line"><a id="l00111" name="l00111"></a><span class="lineno">  111</span>    <span class="comment">/* (Comment taken verbatim from aforementioned `man`.)</span></div>
<div class="line"><a id="l00112" name="l00112"></a><span class="lineno">  112</span><span class="comment">     * Ancillary data buffer, wrapped in a union in order to ensure it is suitably aligned.</span></div>
<div class="line"><a id="l00113" name="l00113"></a><span class="lineno">  113</span><span class="comment">     *</span></div>
<div class="line"><a id="l00114" name="l00114"></a><span class="lineno">  114</span><span class="comment">     * ...If I (ygoldfel) understand correctly, and I think I do, the idea is that:</span></div>
<div class="line"><a id="l00115" name="l00115"></a><span class="lineno">  115</span><span class="comment">     *   - msg_control points to a contiguous data area (ancillary data); which is split up into variable-length</span></div>
<div class="line"><a id="l00116" name="l00116"></a><span class="lineno">  116</span><span class="comment">     *     sub-areas, each of which starts with a header, in the form of a `cmsghdr`, which contains a couple of</span></div>
<div class="line"><a id="l00117" name="l00117"></a><span class="lineno">  117</span><span class="comment">     *     enum-like ints, a cmsg_len specifying the length of the rest of that sub-area (within the sequence),</span></div>
<div class="line"><a id="l00118" name="l00118"></a><span class="lineno">  118</span><span class="comment">     *     and then that area which contains the stuff to be transmitted (whose exact size/meaning depends on the</span></div>
<div class="line"><a id="l00119" name="l00119"></a><span class="lineno">  119</span><span class="comment">     *     enums; in our case it&#39;ll be native handles).</span></div>
<div class="line"><a id="l00120" name="l00120"></a><span class="lineno">  120</span><span class="comment">     *   - A key caveat is that in order to be properly interpreted, the header -- probably cast by the kernel/something</span></div>
<div class="line"><a id="l00121" name="l00121"></a><span class="lineno">  121</span><span class="comment">     *     to `cmsghdr` -- must begin on an aligned address.  So, in particular, if whatever comes before it</span></div>
<div class="line"><a id="l00122" name="l00122"></a><span class="lineno">  122</span><span class="comment">     *     (could be the preceding ancillary data sub-area, depending) ends just before an odd address, then</span></div>
<div class="line"><a id="l00123" name="l00123"></a><span class="lineno">  123</span><span class="comment">     *     the data sub-area must be a byte or a few to the right.</span></div>
<div class="line"><a id="l00124" name="l00124"></a><span class="lineno">  124</span><span class="comment">     *   - So this trick explicitly puts a cmsghdr there; so that its co-inhabitant m_buf (the actual area where we&#39;ll</span></div>
<div class="line"><a id="l00125" name="l00125"></a><span class="lineno">  125</span><span class="comment">     *     shove handles) will also begin on the same address/byte.</span></div>
<div class="line"><a id="l00126" name="l00126"></a><span class="lineno">  126</span><span class="comment">     *   - CMSG_ALIGN() is a Linux extension that might be usable to avoid having to use the trick, but seeing as</span></div>
<div class="line"><a id="l00127" name="l00127"></a><span class="lineno">  127</span><span class="comment">     *     how `man cmsg` in my Linux says it&#39;s not portable and itself foregoes it in favor of the trick in the</span></div>
<div class="line"><a id="l00128" name="l00128"></a><span class="lineno">  128</span><span class="comment">     *     example, I&#39;ll just also use the trick. */</span></div>
<div class="line"><a id="l00129" name="l00129"></a><span class="lineno">  129</span>    array&lt;uint8_t, CMSG_SPACE(<span class="keyword">sizeof</span>(<a class="code hl_typedef" href="structipc_1_1util_1_1Native__handle.html#a7194e8aaf9fc0109aad80222ae4ecb25">Native_handle::handle_t</a>) * N_PAYLOAD_FDS)&gt; m_buf;</div>
<div class="line"><a id="l00130" name="l00130"></a><span class="lineno">  130</span>    cmsghdr m_align;</div>
<div class="line"><a id="l00131" name="l00131"></a><span class="lineno">  131</span>  } msg_control_as_union;</div>
<div class="line"><a id="l00132" name="l00132"></a><span class="lineno">  132</span> </div>
<div class="line"><a id="l00133" name="l00133"></a><span class="lineno">  133</span>  sendmsg_hdr.msg_control = msg_control_as_union.m_buf.c_array();</div>
<div class="line"><a id="l00134" name="l00134"></a><span class="lineno">  134</span>  sendmsg_hdr.msg_controllen = <span class="keyword">sizeof</span>(msg_control_as_union.m_buf);</div>
<div class="line"><a id="l00135" name="l00135"></a><span class="lineno">  135</span>  cmsghdr* <span class="keyword">const</span> sendmsg_hdr_cmsg_ptr = CMSG_FIRSTHDR(&amp;sendmsg_hdr); <span class="comment">// Or cast from &amp;m_buf; or use &amp;m_align....</span></div>
<div class="line"><a id="l00136" name="l00136"></a><span class="lineno">  136</span>  sendmsg_hdr_cmsg_ptr-&gt;cmsg_level = SOL_SOCKET;</div>
<div class="line"><a id="l00137" name="l00137"></a><span class="lineno">  137</span>  sendmsg_hdr_cmsg_ptr-&gt;cmsg_type = SCM_RIGHTS;</div>
<div class="line"><a id="l00138" name="l00138"></a><span class="lineno">  138</span>  sendmsg_hdr_cmsg_ptr-&gt;cmsg_len = CMSG_LEN(<span class="keyword">sizeof</span>(<a class="code hl_typedef" href="structipc_1_1util_1_1Native__handle.html#a7194e8aaf9fc0109aad80222ae4ecb25">Native_handle::handle_t</a>) * N_PAYLOAD_FDS);</div>
<div class="line"><a id="l00139" name="l00139"></a><span class="lineno">  139</span> </div>
<div class="line"><a id="l00140" name="l00140"></a><span class="lineno">  140</span>  <span class="comment">// Copy the FDs.  We have just the one; simply assign (omit `memcpy`) but static_assert() to help future-proof.</span></div>
<div class="line"><a id="l00141" name="l00141"></a><span class="lineno">  141</span>  <span class="keyword">static_assert</span>(N_PAYLOAD_FDS == 1, <span class="stringliteral">&quot;Should be only passing one native handle into sendmsg() as of this writing.&quot;</span>);</div>
<div class="line"><a id="l00142" name="l00142"></a><span class="lineno">  142</span>  *(<span class="keyword">reinterpret_cast&lt;</span><a class="code hl_typedef" href="structipc_1_1util_1_1Native__handle.html#a7194e8aaf9fc0109aad80222ae4ecb25">Native_handle::handle_t</a>*<span class="keyword">&gt;</span>(CMSG_DATA(sendmsg_hdr_cmsg_ptr))) = payload_hndl.<a class="code hl_variable" href="structipc_1_1util_1_1Native__handle.html#ab2f496740139c5752a25a30cf3325d86">m_native_handle</a>;</div>
<div class="line"><a id="l00143" name="l00143"></a><span class="lineno">  143</span> </div>
<div class="line"><a id="l00144" name="l00144"></a><span class="lineno">  144</span>  <span class="keyword">const</span> <span class="keyword">auto</span> n_sent_or_error</div>
<div class="line"><a id="l00145" name="l00145"></a><span class="lineno">  145</span>    = sendmsg(peer_socket.native_handle(), &amp;sendmsg_hdr,</div>
<div class="line"><a id="l00146" name="l00146"></a><span class="lineno">  146</span>              <span class="comment">/* If socket is un-writable then don&#39;t block;</span></div>
<div class="line"><a id="l00147" name="l00147"></a><span class="lineno">  147</span><span class="comment">               * EAGAIN/EWOULDBLOCK instead.  Doing it this way is easier than messing with fcntl(), particularly</span></div>
<div class="line"><a id="l00148" name="l00148"></a><span class="lineno">  148</span><span class="comment">               * since we&#39;re working with a boost.asio-managed socket; that&#39;s actually fine -- there&#39;s a portable</span></div>
<div class="line"><a id="l00149" name="l00149"></a><span class="lineno">  149</span><span class="comment">               * API native_non_blocking() in boost.asio for setting this -- but feels like the less interaction between</span></div>
<div class="line"><a id="l00150" name="l00150"></a><span class="lineno">  150</span><span class="comment">               * portable boost.asio code we use and this native stuff, the better -- so just keep it local here. */</span></div>
<div class="line"><a id="l00151" name="l00151"></a><span class="lineno">  151</span>              MSG_DONTWAIT | MSG_NOSIGNAL);</div>
<div class="line"><a id="l00152" name="l00152"></a><span class="lineno">  152</span>              <span class="comment">// ^-- Dealing with SIGPIPE is a pointless pain; if conn closed that way just give as an EPIPE error.</span></div>
<div class="line"><a id="l00153" name="l00153"></a><span class="lineno">  153</span> </div>
<div class="line"><a id="l00154" name="l00154"></a><span class="lineno">  154</span>  <span class="keywordflow">if</span> (n_sent_or_error == -1)</div>
<div class="line"><a id="l00155" name="l00155"></a><span class="lineno">  155</span>  {</div>
<div class="line"><a id="l00156" name="l00156"></a><span class="lineno">  156</span>    <span class="comment">/* Not even 1 byte of the blob was sent; and hence nor was payload_hndl.  (Docs don&#39;t explicitly say that 2nd</span></div>
<div class="line"><a id="l00157" name="l00157"></a><span class="lineno">  157</span><span class="comment">     * part after the semicolon, but it&#39;s essentially impossible that it be otherwise, as then it&#39;d be unknowable.</span></div>
<div class="line"><a id="l00158" name="l00158"></a><span class="lineno">  158</span><span class="comment">     * Update: Confirmed in kernel source and supported by this delightfully reassuring (in several ways) link:</span></div>
<div class="line"><a id="l00159" name="l00159"></a><span class="lineno">  159</span><span class="comment">     * [ https://gist.github.com/kentonv/bc7592af98c68ba2738f4436920868dc ] (Googled &quot;SCM_RIGHTS gist&quot;).) */</span></div>
<div class="line"><a id="l00160" name="l00160"></a><span class="lineno">  160</span> </div>
<div class="line"><a id="l00161" name="l00161"></a><span class="lineno">  161</span>    <span class="keyword">const</span> <a class="code hl_typedef" href="namespaceipc.html#aa3192e586cc45d3e7c22463bf2760f89">Error_code</a> sys_err_code(errno, system_category());</div>
<div class="line"><a id="l00162" name="l00162"></a><span class="lineno">  162</span>    <span class="keywordflow">if</span> ((sys_err_code == sys_err_codes::operation_would_block) || <span class="comment">// EWOULDBLOCK</span></div>
<div class="line"><a id="l00163" name="l00163"></a><span class="lineno">  163</span>        (sys_err_code == sys_err_codes::resource_unavailable_try_again)) <span class="comment">// EAGAIN (same meaning)</span></div>
<div class="line"><a id="l00164" name="l00164"></a><span class="lineno">  164</span>    {</div>
<div class="line"><a id="l00165" name="l00165"></a><span class="lineno">  165</span>      FLOW_LOG_TRACE(<span class="stringliteral">&quot;Write attempt indicated would-block; not an error condition.  Nothing sent.&quot;</span>);</div>
<div class="line"><a id="l00166" name="l00166"></a><span class="lineno">  166</span>      <span class="comment">/* Subtlety: We could just set it to sys_err_code; but we specifically promised in contract we&#39;d set it to the</span></div>
<div class="line"><a id="l00167" name="l00167"></a><span class="lineno">  167</span><span class="comment">       * boost::asio::error::would_block representation of would-block condition.  Why did we promise that?  2 reasons:</span></div>
<div class="line"><a id="l00168" name="l00168"></a><span class="lineno">  168</span><span class="comment">       * 1, that is what boost.asio&#39;s own spiritually similar Peer_socket::write_some() would do in non_blocking() mode.</span></div>
<div class="line"><a id="l00169" name="l00169"></a><span class="lineno">  169</span><span class="comment">       * 2, then we can promise a specific code instead of making them check for the above 2 errno values.</span></div>
<div class="line"><a id="l00170" name="l00170"></a><span class="lineno">  170</span><span class="comment">       *</span></div>
<div class="line"><a id="l00171" name="l00171"></a><span class="lineno">  171</span><span class="comment">       * Subtlety: net_flow::Peer_socket::sync_receive uses somewhat different semantics; it indicates would-block by</span></div>
<div class="line"><a id="l00172" name="l00172"></a><span class="lineno">  172</span><span class="comment">       * returning 0 *but* a falsy *err_code.  Why are we inconsistent with that?  Answer: Because net_flow is not</span></div>
<div class="line"><a id="l00173" name="l00173"></a><span class="lineno">  173</span><span class="comment">       * trying to be a boost.asio extension; we are.  In net_flow&#39;s context (as of this writing) no one is surprised</span></div>
<div class="line"><a id="l00174" name="l00174"></a><span class="lineno">  174</span><span class="comment">       * when semantics are somewhat different from boost.asio; but in our context they might be quite surprised</span></div>
<div class="line"><a id="l00175" name="l00175"></a><span class="lineno">  175</span><span class="comment">       * indeed. */</span></div>
<div class="line"><a id="l00176" name="l00176"></a><span class="lineno">  176</span>      *err_code = boost::asio::error::would_block;</div>
<div class="line"><a id="l00177" name="l00177"></a><span class="lineno">  177</span>      <span class="keywordflow">return</span> 0;</div>
<div class="line"><a id="l00178" name="l00178"></a><span class="lineno">  178</span>    }</div>
<div class="line"><a id="l00179" name="l00179"></a><span class="lineno">  179</span>    <span class="comment">// else</span></div>
<div class="line"><a id="l00180" name="l00180"></a><span class="lineno">  180</span> </div>
<div class="line"><a id="l00181" name="l00181"></a><span class="lineno">  181</span>    assert(sys_err_code);</div>
<div class="line"><a id="l00182" name="l00182"></a><span class="lineno">  182</span> </div>
<div class="line"><a id="l00183" name="l00183"></a><span class="lineno">  183</span>    <span class="comment">// All other errors are fatal.</span></div>
<div class="line"><a id="l00184" name="l00184"></a><span class="lineno">  184</span>    FLOW_ERROR_SYS_ERROR_LOG_WARNING(); <span class="comment">// Log based on sys_err_code.</span></div>
<div class="line"><a id="l00185" name="l00185"></a><span class="lineno">  185</span>    FLOW_LOG_WARNING(<span class="stringliteral">&quot;Connected local peer socket tried to write from &quot;</span></div>
<div class="line"><a id="l00186" name="l00186"></a><span class="lineno">  186</span>                     <span class="stringliteral">&quot;location @ [&quot;</span> &lt;&lt; payload_blob.data() &lt;&lt; <span class="stringliteral">&quot;] plus native handle [&quot;</span> &lt;&lt; payload_hndl &lt;&lt; <span class="stringliteral">&quot;]; &quot;</span></div>
<div class="line"><a id="l00187" name="l00187"></a><span class="lineno">  187</span>                     <span class="stringliteral">&quot;but an unrecoverable error occurred.  Nothing sent.&quot;</span>);</div>
<div class="line"><a id="l00188" name="l00188"></a><span class="lineno">  188</span>    *err_code = sys_err_code;</div>
<div class="line"><a id="l00189" name="l00189"></a><span class="lineno">  189</span>    <span class="keywordflow">return</span> 0;</div>
<div class="line"><a id="l00190" name="l00190"></a><span class="lineno">  190</span>  } <span class="comment">// if (n_sent_or_error == -1)</span></div>
<div class="line"><a id="l00191" name="l00191"></a><span class="lineno">  191</span>  <span class="comment">// else if (n_sent_or_error != -1)</span></div>
<div class="line"><a id="l00192" name="l00192"></a><span class="lineno">  192</span> </div>
<div class="line"><a id="l00193" name="l00193"></a><span class="lineno">  193</span>  assert (n_sent_or_error &gt; 0);</div>
<div class="line"><a id="l00194" name="l00194"></a><span class="lineno">  194</span> </div>
<div class="line"><a id="l00195" name="l00195"></a><span class="lineno">  195</span>  FLOW_LOG_TRACE(<span class="stringliteral">&quot;sendmsg() reports the native handle [&quot;</span> &lt;&lt; payload_hndl &lt;&lt; <span class="stringliteral">&quot;] was successfully sent; as &quot;</span></div>
<div class="line"><a id="l00196" name="l00196"></a><span class="lineno">  196</span>                 <span class="stringliteral">&quot;were [&quot;</span> &lt;&lt; n_sent_or_error &lt;&lt; <span class="stringliteral">&quot;] of the blob&#39;s [&quot;</span> &lt;&lt; payload_blob.size() &lt;&lt; <span class="stringliteral">&quot;] bytes.&quot;</span>);</div>
<div class="line"><a id="l00197" name="l00197"></a><span class="lineno">  197</span>  err_code-&gt;clear();</div>
<div class="line"><a id="l00198" name="l00198"></a><span class="lineno">  198</span>  <span class="keywordflow">return</span> n_sent_or_error;</div>
<div class="line"><a id="l00199" name="l00199"></a><span class="lineno">  199</span>} <span class="comment">// nb_write_some_with_native_handle()</span></div>
<div class="line"><a id="l00200" name="l00200"></a><span class="lineno">  200</span> </div>
<div class="line"><a id="l00201" name="l00201"></a><span class="lineno"><a class="line" href="namespaceipc_1_1transport_1_1asio__local__stream__socket.html#a9ae82b2a234b218704c62fb616d6fcc5">  201</a></span><span class="keywordtype">size_t</span> <a class="code hl_function" href="namespaceipc_1_1transport_1_1asio__local__stream__socket.html#a9ae82b2a234b218704c62fb616d6fcc5">nb_read_some_with_native_handle</a>(flow::log::Logger* logger_ptr,</div>
<div class="line"><a id="l00202" name="l00202"></a><span class="lineno">  202</span>                                       <a class="code hl_typedef" href="namespaceipc_1_1transport_1_1asio__local__stream__socket.html#a1788f9dbd896bb71b3693f9ae25b40ae">Peer_socket</a>* peer_socket_ptr,</div>
<div class="line"><a id="l00203" name="l00203"></a><span class="lineno">  203</span>                                       <a class="code hl_struct" href="structipc_1_1util_1_1Native__handle.html">Native_handle</a>* target_payload_hndl_ptr,</div>
<div class="line"><a id="l00204" name="l00204"></a><span class="lineno">  204</span>                                       <span class="keyword">const</span> <a class="code hl_typedef" href="namespaceipc_1_1util.html#a6cb62ae434900f3a8915b33ec5d61a96">util::Blob_mutable</a>&amp; target_payload_blob,</div>
<div class="line"><a id="l00205" name="l00205"></a><span class="lineno">  205</span>                                       <a class="code hl_typedef" href="namespaceipc.html#aa3192e586cc45d3e7c22463bf2760f89">Error_code</a>* err_code,</div>
<div class="line"><a id="l00206" name="l00206"></a><span class="lineno">  206</span>                                       <span class="keywordtype">int</span> message_flags)</div>
<div class="line"><a id="l00207" name="l00207"></a><span class="lineno">  207</span>{</div>
<div class="line"><a id="l00208" name="l00208"></a><span class="lineno">  208</span>  <span class="keyword">using </span>boost::system::system_category;</div>
<div class="line"><a id="l00209" name="l00209"></a><span class="lineno">  209</span>  <span class="keyword">using </span>boost::array;</div>
<div class="line"><a id="l00210" name="l00210"></a><span class="lineno">  210</span>  <span class="keyword">namespace </span>sys_err_codes = boost::system::errc;</div>
<div class="line"><a id="l00211" name="l00211"></a><span class="lineno">  211</span>  using ::sendmsg;</div>
<div class="line"><a id="l00212" name="l00212"></a><span class="lineno">  212</span>  using ::msghdr;</div>
<div class="line"><a id="l00213" name="l00213"></a><span class="lineno">  213</span>  using ::iovec;</div>
<div class="line"><a id="l00214" name="l00214"></a><span class="lineno">  214</span>  using ::cmsghdr;</div>
<div class="line"><a id="l00215" name="l00215"></a><span class="lineno">  215</span>  <span class="comment">// using ::SOL_SOCKET; // It&#39;s a macro apparently.</span></div>
<div class="line"><a id="l00216" name="l00216"></a><span class="lineno">  216</span>  using ::SCM_RIGHTS;</div>
<div class="line"><a id="l00217" name="l00217"></a><span class="lineno">  217</span>  using ::MSG_DONTWAIT;</div>
<div class="line"><a id="l00218" name="l00218"></a><span class="lineno">  218</span>  using ::MSG_CTRUNC;</div>
<div class="line"><a id="l00219" name="l00219"></a><span class="lineno">  219</span>  <span class="comment">// using ::errno; // It&#39;s a macro apparently.</span></div>
<div class="line"><a id="l00220" name="l00220"></a><span class="lineno">  220</span> </div>
<div class="line"><a id="l00221" name="l00221"></a><span class="lineno">  221</span>  FLOW_ERROR_EXEC_AND_THROW_ON_ERROR(<span class="keywordtype">size_t</span>, <a class="code hl_function" href="namespaceipc_1_1transport_1_1asio__local__stream__socket.html#a9ae82b2a234b218704c62fb616d6fcc5">nb_read_some_with_native_handle</a>,</div>
<div class="line"><a id="l00222" name="l00222"></a><span class="lineno">  222</span>                                     logger_ptr, peer_socket_ptr, target_payload_hndl_ptr,</div>
<div class="line"><a id="l00223" name="l00223"></a><span class="lineno">  223</span>                                     target_payload_blob, _1, message_flags);</div>
<div class="line"><a id="l00224" name="l00224"></a><span class="lineno">  224</span>  <span class="comment">// ^-- Call ourselves and return if err_code is null.  If got to present line, err_code is not null.</span></div>
<div class="line"><a id="l00225" name="l00225"></a><span class="lineno">  225</span> </div>
<div class="line"><a id="l00226" name="l00226"></a><span class="lineno">  226</span>  <span class="comment">/* To reader/maintainer: The below isn&#39;t that difficult, but if you need exact understanding and definitely if you</span></div>
<div class="line"><a id="l00227" name="l00227"></a><span class="lineno">  227</span><span class="comment">   * plan to make changes -- even just clarifications or changes in the doc header -- then read the entire doc header</span></div>
<div class="line"><a id="l00228" name="l00228"></a><span class="lineno">  228</span><span class="comment">   * of nb_read_some_with_native_handle() first. */</span></div>
<div class="line"><a id="l00229" name="l00229"></a><span class="lineno">  229</span> </div>
<div class="line"><a id="l00230" name="l00230"></a><span class="lineno">  230</span>  assert(peer_socket_ptr);</div>
<div class="line"><a id="l00231" name="l00231"></a><span class="lineno">  231</span>  assert(target_payload_hndl_ptr);</div>
<div class="line"><a id="l00232" name="l00232"></a><span class="lineno">  232</span> </div>
<div class="line"><a id="l00233" name="l00233"></a><span class="lineno">  233</span>  <span class="keyword">auto</span>&amp; peer_socket = *peer_socket_ptr;</div>
<div class="line"><a id="l00234" name="l00234"></a><span class="lineno">  234</span>  <span class="keyword">auto</span>&amp; target_payload_hndl = *target_payload_hndl_ptr;</div>
<div class="line"><a id="l00235" name="l00235"></a><span class="lineno">  235</span> </div>
<div class="line"><a id="l00236" name="l00236"></a><span class="lineno">  236</span>  FLOW_LOG_SET_CONTEXT(logger_ptr, Log_component::S_TRANSPORT);</div>
<div class="line"><a id="l00237" name="l00237"></a><span class="lineno">  237</span>  FLOW_LOG_TRACE(<span class="stringliteral">&quot;Connected local peer socket wants to read up to [&quot;</span> &lt;&lt; target_payload_blob.size() &lt;&lt; <span class="stringliteral">&quot;] bytes &quot;</span></div>
<div class="line"><a id="l00238" name="l00238"></a><span class="lineno">  238</span>                 <span class="stringliteral">&quot;to location @ [&quot;</span> &lt;&lt; target_payload_blob.data() &lt;&lt; <span class="stringliteral">&quot;] &quot;</span></div>
<div class="line"><a id="l00239" name="l00239"></a><span class="lineno">  239</span>                 <span class="stringliteral">&quot;plus possibly a native handle.  Will try to receive.&quot;</span>);</div>
<div class="line"><a id="l00240" name="l00240"></a><span class="lineno">  240</span>  target_payload_hndl = <a class="code hl_typedef" href="namespaceipc_1_1transport.html#a7ee4551983d9df16ec16a3139bac50e8">Native_handle</a>();</div>
<div class="line"><a id="l00241" name="l00241"></a><span class="lineno">  241</span>  assert(target_payload_hndl.null()); <span class="comment">// We promised to set to this if no socket received (including on error).</span></div>
<div class="line"><a id="l00242" name="l00242"></a><span class="lineno">  242</span> </div>
<div class="line"><a id="l00243" name="l00243"></a><span class="lineno">  243</span>  <span class="comment">/* Let us receive as much as possible into target_payload_blob up to its size; and a native socket (if any) into</span></div>
<div class="line"><a id="l00244" name="l00244"></a><span class="lineno">  244</span><span class="comment">   * target_payload_hndl (if none, then it&#39;ll remain null()).</span></div>
<div class="line"><a id="l00245" name="l00245"></a><span class="lineno">  245</span><span class="comment">   * As explicitly documented in boost.asio docs: it does not provide an API for the latter (fairly hairy</span></div>
<div class="line"><a id="l00246" name="l00246"></a><span class="lineno">  246</span><span class="comment">   * and Linux-specific) feature, but it is doable by using recvmsg() natively via peer_socket.native_handle()</span></div>
<div class="line"><a id="l00247" name="l00247"></a><span class="lineno">  247</span><span class="comment">   * which gets the native handle (a/k/a FD).</span></div>
<div class="line"><a id="l00248" name="l00248"></a><span class="lineno">  248</span><span class="comment">   *</span></div>
<div class="line"><a id="l00249" name="l00249"></a><span class="lineno">  249</span><span class="comment">   * Recommending first looking at nb_write_some_with_native_handle(), as we operate symmetrically/similarly. */</span></div>
<div class="line"><a id="l00250" name="l00250"></a><span class="lineno">  250</span> </div>
<div class="line"><a id="l00251" name="l00251"></a><span class="lineno">  251</span>  iovec native_buf1 = { target_payload_blob.data(), target_payload_blob.size() };</div>
<div class="line"><a id="l00252" name="l00252"></a><span class="lineno">  252</span>  msghdr recvmsg_hdr =</div>
<div class="line"><a id="l00253" name="l00253"></a><span class="lineno">  253</span>  {</div>
<div class="line"><a id="l00254" name="l00254"></a><span class="lineno">  254</span>     0, <span class="comment">// msg_name - Address; not used; we are connected.</span></div>
<div class="line"><a id="l00255" name="l00255"></a><span class="lineno">  255</span>     0, <span class="comment">// msg_namelen - Ditto.</span></div>
<div class="line"><a id="l00256" name="l00256"></a><span class="lineno">  256</span>     <span class="comment">/* msg_iov - Scatter/gather array.  We just put the one target blob here.  See similarly-themed notes at similar</span></div>
<div class="line"><a id="l00257" name="l00257"></a><span class="lineno">  257</span><span class="comment">      * spot in nb_write_some_with_native_handle(); they apply here too, more or less. */</span></div>
<div class="line"><a id="l00258" name="l00258"></a><span class="lineno">  258</span>     &amp;native_buf1,</div>
<div class="line"><a id="l00259" name="l00259"></a><span class="lineno">  259</span>     1, <span class="comment">// msg_iovlen - # elements in msg_iov.  This is an *input* arg only; output is total length read: the ret value.</span></div>
<div class="line"><a id="l00260" name="l00260"></a><span class="lineno">  260</span>     <span class="comment">/* The following fields may or may need not be initialized; but let&#39;s discuss them generally:</span></div>
<div class="line"><a id="l00261" name="l00261"></a><span class="lineno">  261</span><span class="comment">      * msg_control, msg_controllen - These are out-args, indirectly set/reserved and interpreted with CMSG* below.</span></div>
<div class="line"><a id="l00262" name="l00262"></a><span class="lineno">  262</span><span class="comment">      * msg_flags - This is an out-arg containing special feature flags.  These may be checked below after call.</span></div>
<div class="line"><a id="l00263" name="l00263"></a><span class="lineno">  263</span><span class="comment">      * The language won&#39;t let me leave them as garbage though so: */</span></div>
<div class="line"><a id="l00264" name="l00264"></a><span class="lineno">  264</span>     0, 0, 0</div>
<div class="line"><a id="l00265" name="l00265"></a><span class="lineno">  265</span>  };</div>
<div class="line"><a id="l00266" name="l00266"></a><span class="lineno">  266</span>  <span class="comment">// May not be needed, but at least some examples online do it; seems prudent and cheap.</span></div>
<div class="line"><a id="l00267" name="l00267"></a><span class="lineno">  267</span>  recvmsg_hdr.msg_flags = 0;</div>
<div class="line"><a id="l00268" name="l00268"></a><span class="lineno">  268</span> </div>
<div class="line"><a id="l00269" name="l00269"></a><span class="lineno">  269</span>  <span class="comment">/* Set up .msg_control*.  This, and then interpreting the output after the call, is based on the out-equivalent in</span></div>
<div class="line"><a id="l00270" name="l00270"></a><span class="lineno">  270</span><span class="comment">   * nb_write_some_with_native_handle() as well as cross-referencing with some Internet sources.</span></div>
<div class="line"><a id="l00271" name="l00271"></a><span class="lineno">  271</span><span class="comment">   *</span></div>
<div class="line"><a id="l00272" name="l00272"></a><span class="lineno">  272</span><span class="comment">   * Before the call, we must reserve space for the ancillary out-data, if any; set msg_control to point to that;</span></div>
<div class="line"><a id="l00273" name="l00273"></a><span class="lineno">  273</span><span class="comment">   * and msg_controllen to the size of that thing. */</span></div>
<div class="line"><a id="l00274" name="l00274"></a><span class="lineno">  274</span> </div>
<div class="line"><a id="l00275" name="l00275"></a><span class="lineno">  275</span>  <span class="keyword">constexpr</span> <span class="keywordtype">size_t</span> N_PAYLOAD_FDS = 1;</div>
<div class="line"><a id="l00276" name="l00276"></a><span class="lineno">  276</span>  <span class="keyword">union</span></div>
<div class="line"><a id="l00277" name="l00277"></a><span class="lineno">  277</span>  {</div>
<div class="line"><a id="l00278" name="l00278"></a><span class="lineno">  278</span>    <span class="comment">// See nb_write_some_with_native_handle().  It explains the m_align thing.</span></div>
<div class="line"><a id="l00279" name="l00279"></a><span class="lineno">  279</span>    array&lt;uint8_t, CMSG_SPACE(<span class="keyword">sizeof</span>(<a class="code hl_typedef" href="structipc_1_1util_1_1Native__handle.html#a7194e8aaf9fc0109aad80222ae4ecb25">Native_handle::handle_t</a>) * N_PAYLOAD_FDS)&gt; m_buf;</div>
<div class="line"><a id="l00280" name="l00280"></a><span class="lineno">  280</span>    cmsghdr m_align;</div>
<div class="line"><a id="l00281" name="l00281"></a><span class="lineno">  281</span>  } msg_control_as_union;</div>
<div class="line"><a id="l00282" name="l00282"></a><span class="lineno">  282</span>  <span class="comment">// Probably paranoia.  Just in case pre-fill it with zeroes (0x00... is not a valid FD) for sanity check later.</span></div>
<div class="line"><a id="l00283" name="l00283"></a><span class="lineno">  283</span>  msg_control_as_union.m_buf.fill(0);</div>
<div class="line"><a id="l00284" name="l00284"></a><span class="lineno">  284</span> </div>
<div class="line"><a id="l00285" name="l00285"></a><span class="lineno">  285</span>  recvmsg_hdr.msg_control = msg_control_as_union.m_buf.c_array();</div>
<div class="line"><a id="l00286" name="l00286"></a><span class="lineno">  286</span>  recvmsg_hdr.msg_controllen = <span class="keyword">sizeof</span>(msg_control_as_union.m_buf);</div>
<div class="line"><a id="l00287" name="l00287"></a><span class="lineno">  287</span> </div>
<div class="line"><a id="l00288" name="l00288"></a><span class="lineno">  288</span>  <span class="keyword">const</span> <span class="keyword">auto</span> n_rcvd_or_error</div>
<div class="line"><a id="l00289" name="l00289"></a><span class="lineno">  289</span>    = recvmsg(peer_socket.native_handle(), &amp;recvmsg_hdr,</div>
<div class="line"><a id="l00290" name="l00290"></a><span class="lineno">  290</span>              <span class="comment">/* If socket is un-writable then don&#39;t block; EAGAIN/EWOULDBLOCK instead. ...Further comment omitted;</span></div>
<div class="line"><a id="l00291" name="l00291"></a><span class="lineno">  291</span><span class="comment">               * see sendmsg() elsewhere in this .cpp.  Same thing here. */</span></div>
<div class="line"><a id="l00292" name="l00292"></a><span class="lineno">  292</span>              MSG_DONTWAIT | message_flags); <span class="comment">// &lt;-- Re. message_flags please read notes in our doc header.</span></div>
<div class="line"><a id="l00293" name="l00293"></a><span class="lineno">  293</span> </div>
<div class="line"><a id="l00294" name="l00294"></a><span class="lineno">  294</span>  <span class="comment">// Carefully check all the outputs.  Return value first.</span></div>
<div class="line"><a id="l00295" name="l00295"></a><span class="lineno">  295</span> </div>
<div class="line"><a id="l00296" name="l00296"></a><span class="lineno">  296</span>  <span class="keywordflow">if</span> (n_rcvd_or_error == -1)</div>
<div class="line"><a id="l00297" name="l00297"></a><span class="lineno">  297</span>  {</div>
<div class="line"><a id="l00298" name="l00298"></a><span class="lineno">  298</span>    <span class="comment">/* Not even 1 byte of a blob was read; and hence nor was any target_payload_hndl.  (See comment in similar</span></div>
<div class="line"><a id="l00299" name="l00299"></a><span class="lineno">  299</span><span class="comment">     * sport in nb_write_some_with_native_handle(); applies here equally.) */</span></div>
<div class="line"><a id="l00300" name="l00300"></a><span class="lineno">  300</span> </div>
<div class="line"><a id="l00301" name="l00301"></a><span class="lineno">  301</span>    <span class="keyword">const</span> <a class="code hl_typedef" href="namespaceipc.html#aa3192e586cc45d3e7c22463bf2760f89">Error_code</a> sys_err_code(errno, system_category());</div>
<div class="line"><a id="l00302" name="l00302"></a><span class="lineno">  302</span>    <span class="keywordflow">if</span> ((sys_err_code == sys_err_codes::operation_would_block) || <span class="comment">// EWOULDBLOCK</span></div>
<div class="line"><a id="l00303" name="l00303"></a><span class="lineno">  303</span>        (sys_err_code == sys_err_codes::resource_unavailable_try_again)) <span class="comment">// EAGAIN (same meaning)</span></div>
<div class="line"><a id="l00304" name="l00304"></a><span class="lineno">  304</span>    <span class="comment">/* Reader: &quot;But, ygoldfel, why didn&#39;t you just check errno itself against those 2 actual Evalues?&quot;</span></div>
<div class="line"><a id="l00305" name="l00305"></a><span class="lineno">  305</span><span class="comment">     * ygoldfel: &quot;Because it makes me feel better about portable-ish style.  Shut up, that&#39;s why.  Get off my lawn.&quot; */</span></div>
<div class="line"><a id="l00306" name="l00306"></a><span class="lineno">  306</span>    {</div>
<div class="line"><a id="l00307" name="l00307"></a><span class="lineno">  307</span>      FLOW_LOG_TRACE(<span class="stringliteral">&quot;Read attempt indicated would-block; not an error condition.  Nothing received.&quot;</span>);</div>
<div class="line"><a id="l00308" name="l00308"></a><span class="lineno">  308</span>      <span class="comment">// Subtlety x 2: ...omitted.  See similar spot in nb_write_some_with_native_handle().  Same here.</span></div>
<div class="line"><a id="l00309" name="l00309"></a><span class="lineno">  309</span>      *err_code = boost::asio::error::would_block;</div>
<div class="line"><a id="l00310" name="l00310"></a><span class="lineno">  310</span>      <span class="keywordflow">return</span> 0; <span class="comment">// target_payload_hndl already set.</span></div>
<div class="line"><a id="l00311" name="l00311"></a><span class="lineno">  311</span>    }</div>
<div class="line"><a id="l00312" name="l00312"></a><span class="lineno">  312</span>    <span class="comment">// else</span></div>
<div class="line"><a id="l00313" name="l00313"></a><span class="lineno">  313</span> </div>
<div class="line"><a id="l00314" name="l00314"></a><span class="lineno">  314</span>    assert(sys_err_code);</div>
<div class="line"><a id="l00315" name="l00315"></a><span class="lineno">  315</span> </div>
<div class="line"><a id="l00316" name="l00316"></a><span class="lineno">  316</span>    <span class="comment">// All other errors are fatal.</span></div>
<div class="line"><a id="l00317" name="l00317"></a><span class="lineno">  317</span>    FLOW_ERROR_SYS_ERROR_LOG_WARNING(); <span class="comment">// Log based on sys_err_code.</span></div>
<div class="line"><a id="l00318" name="l00318"></a><span class="lineno">  318</span>    FLOW_LOG_WARNING(<span class="stringliteral">&quot;Connected local peer socket tried to read up to [&quot;</span> &lt;&lt; target_payload_blob.size() &lt;&lt; <span class="stringliteral">&quot;] bytes at &quot;</span></div>
<div class="line"><a id="l00319" name="l00319"></a><span class="lineno">  319</span>                     <span class="stringliteral">&quot;location @ [&quot;</span> &lt;&lt; target_payload_blob.data() &lt;&lt; <span class="stringliteral">&quot;] plus possibly a native handle; &quot;</span></div>
<div class="line"><a id="l00320" name="l00320"></a><span class="lineno">  320</span>                     <span class="stringliteral">&quot;but an unrecoverable error occurred.  Nothing received.&quot;</span>);</div>
<div class="line"><a id="l00321" name="l00321"></a><span class="lineno">  321</span>    *err_code = sys_err_code;</div>
<div class="line"><a id="l00322" name="l00322"></a><span class="lineno">  322</span>    <span class="keywordflow">return</span> 0; <span class="comment">// target_payload_hndl already set.</span></div>
<div class="line"><a id="l00323" name="l00323"></a><span class="lineno">  323</span>  } <span class="comment">// if (n_rcvd_or_error == -1)</span></div>
<div class="line"><a id="l00324" name="l00324"></a><span class="lineno">  324</span>  <span class="comment">// else if (n_rcvd_or_error != -1)</span></div>
<div class="line"><a id="l00325" name="l00325"></a><span class="lineno">  325</span> </div>
<div class="line"><a id="l00326" name="l00326"></a><span class="lineno">  326</span>  <span class="keywordflow">if</span> (n_rcvd_or_error == 0)</div>
<div class="line"><a id="l00327" name="l00327"></a><span class="lineno">  327</span>  {</div>
<div class="line"><a id="l00328" name="l00328"></a><span class="lineno">  328</span>    <span class="comment">/* WARNING doesn&#39;t feel right: it&#39;s a graceful connection end.</span></div>
<div class="line"><a id="l00329" name="l00329"></a><span class="lineno">  329</span><span class="comment">     * INFO could be good, but it might be too verbose depending on the application.</span></div>
<div class="line"><a id="l00330" name="l00330"></a><span class="lineno">  330</span><span class="comment">     * Use TRACE to be safe; caller can always log differently if desired. */</span></div>
<div class="line"><a id="l00331" name="l00331"></a><span class="lineno">  331</span>    FLOW_LOG_TRACE(<span class="stringliteral">&quot;Connected local peer socket tried to read up to [&quot;</span> &lt;&lt; target_payload_blob.size() &lt;&lt; <span class="stringliteral">&quot;] bytes at &quot;</span></div>
<div class="line"><a id="l00332" name="l00332"></a><span class="lineno">  332</span>                   <span class="stringliteral">&quot;location @ [&quot;</span> &lt;&lt; target_payload_blob.data() &lt;&lt; <span class="stringliteral">&quot;] plus possibly a native handle; &quot;</span></div>
<div class="line"><a id="l00333" name="l00333"></a><span class="lineno">  333</span>                   <span class="stringliteral">&quot;but it returned EOF meaning orderly connection shutdown by peer.  Nothing received.&quot;</span>);</div>
<div class="line"><a id="l00334" name="l00334"></a><span class="lineno">  334</span>    *err_code = boost::asio::error::eof;</div>
<div class="line"><a id="l00335" name="l00335"></a><span class="lineno">  335</span>    <span class="keywordflow">return</span> 0; <span class="comment">// target_payload_hndl already set.</span></div>
<div class="line"><a id="l00336" name="l00336"></a><span class="lineno">  336</span>  }</div>
<div class="line"><a id="l00337" name="l00337"></a><span class="lineno">  337</span>  <span class="comment">// else</span></div>
<div class="line"><a id="l00338" name="l00338"></a><span class="lineno">  338</span>  assert(n_rcvd_or_error &gt; 0);</div>
<div class="line"><a id="l00339" name="l00339"></a><span class="lineno">  339</span> </div>
<div class="line"><a id="l00340" name="l00340"></a><span class="lineno">  340</span>  <span class="comment">/* Next, target_payload_blob... which is already written to (its first n_rcvd_or_error bytes).</span></div>
<div class="line"><a id="l00341" name="l00341"></a><span class="lineno">  341</span><span class="comment">   *</span></div>
<div class="line"><a id="l00342" name="l00342"></a><span class="lineno">  342</span><span class="comment">   * Next, recvmsg_hdr.msg_flags.  Basically only the following is relevant: */</span></div>
<div class="line"><a id="l00343" name="l00343"></a><span class="lineno">  343</span>  <span class="keywordflow">if</span> (recvmsg_hdr.msg_flags != 0)</div>
<div class="line"><a id="l00344" name="l00344"></a><span class="lineno">  344</span>  {</div>
<div class="line"><a id="l00345" name="l00345"></a><span class="lineno">  345</span>    FLOW_LOG_INFO(<span class="stringliteral">&quot;Connected local peer socket tried to read up to [&quot;</span> &lt;&lt; target_payload_blob.size() &lt;&lt; <span class="stringliteral">&quot;] bytes at &quot;</span></div>
<div class="line"><a id="l00346" name="l00346"></a><span class="lineno">  346</span>                  <span class="stringliteral">&quot;location @ [&quot;</span> &lt;&lt; target_payload_blob.data() &lt;&lt; <span class="stringliteral">&quot;] plus possibly a native handle; &quot;</span></div>
<div class="line"><a id="l00347" name="l00347"></a><span class="lineno">  347</span>                  <span class="stringliteral">&quot;and it returned it read [&quot;</span> &lt;&lt; n_rcvd_or_error &lt;&lt; <span class="stringliteral">&quot;] bytes successfully but also returned raw &quot;</span></div>
<div class="line"><a id="l00348" name="l00348"></a><span class="lineno">  348</span>                  <span class="stringliteral">&quot;out-flags value [0x&quot;</span> &lt;&lt; std::hex &lt;&lt; recvmsg_hdr.msg_flags &lt;&lt; std::dec &lt;&lt; <span class="stringliteral">&quot;].  &quot;</span></div>
<div class="line"><a id="l00349" name="l00349"></a><span class="lineno">  349</span>                  <span class="stringliteral">&quot;Will check for relevant flags but otherwise &quot;</span></div>
<div class="line"><a id="l00350" name="l00350"></a><span class="lineno">  350</span>                  <span class="stringliteral">&quot;ignoring if nothing bad.  Logging at elevated level because it&#39;s interesting; please investigate.&quot;</span>);</div>
<div class="line"><a id="l00351" name="l00351"></a><span class="lineno">  351</span> </div>
<div class="line"><a id="l00352" name="l00352"></a><span class="lineno">  352</span>    <span class="keywordflow">if</span> ((recvmsg_hdr.msg_flags &amp; MSG_CTRUNC) != 0)</div>
<div class="line"><a id="l00353" name="l00353"></a><span class="lineno">  353</span>    {</div>
<div class="line"><a id="l00354" name="l00354"></a><span class="lineno">  354</span>      FLOW_LOG_WARNING(<span class="stringliteral">&quot;Connected local peer socket tried to read up to [&quot;</span> &lt;&lt; target_payload_blob.size() &lt;&lt; <span class="stringliteral">&quot;] bytes &quot;</span></div>
<div class="line"><a id="l00355" name="l00355"></a><span class="lineno">  355</span>                       <span class="stringliteral">&quot;at location @ [&quot;</span> &lt;&lt; target_payload_blob.data() &lt;&lt; <span class="stringliteral">&quot;] plus possibly a native handle; &quot;</span></div>
<div class="line"><a id="l00356" name="l00356"></a><span class="lineno">  356</span>                       <span class="stringliteral">&quot;and it returned it read [&quot;</span> &lt;&lt; n_rcvd_or_error &lt;&lt; <span class="stringliteral">&quot;] bytes successfully but also returned raw &quot;</span></div>
<div class="line"><a id="l00357" name="l00357"></a><span class="lineno">  357</span>                       <span class="stringliteral">&quot;out-flags value [0x&quot;</span> &lt;&lt; recvmsg_hdr.msg_flags &lt;&lt; <span class="stringliteral">&quot;] which includes MSG_CTRUNC.  &quot;</span></div>
<div class="line"><a id="l00358" name="l00358"></a><span class="lineno">  358</span>                       <span class="stringliteral">&quot;That flag indicates more stuff was sent as ancillary data; but we expect at most 1 native &quot;</span></div>
<div class="line"><a id="l00359" name="l00359"></a><span class="lineno">  359</span>                       <span class="stringliteral">&quot;handle.  Other side sent something strange.  Acting as if nothing received + error.&quot;</span>);</div>
<div class="line"><a id="l00360" name="l00360"></a><span class="lineno">  360</span>      *err_code = <a class="code hl_enumvalue" href="namespaceipc_1_1transport_1_1error.html#adfef15ef4e76cc55d652fbd9c2797297a8c068cf7b73b09b5ed3fa3532de1747c">error::Code::S_LOW_LVL_UNEXPECTED_STREAM_PAYLOAD_BEYOND_HNDL</a>;</div>
<div class="line"><a id="l00361" name="l00361"></a><span class="lineno">  361</span>      <span class="keywordflow">return</span> 0; <span class="comment">// target_payload_hndl already set.</span></div>
<div class="line"><a id="l00362" name="l00362"></a><span class="lineno">  362</span>    }</div>
<div class="line"><a id="l00363" name="l00363"></a><span class="lineno">  363</span>    <span class="comment">// else</span></div>
<div class="line"><a id="l00364" name="l00364"></a><span class="lineno">  364</span>  }</div>
<div class="line"><a id="l00365" name="l00365"></a><span class="lineno">  365</span> </div>
<div class="line"><a id="l00366" name="l00366"></a><span class="lineno">  366</span>  <span class="comment">/* Lastly examine ancillary data (and note MSG_CTRUNC already eliminated above).</span></div>
<div class="line"><a id="l00367" name="l00367"></a><span class="lineno">  367</span><span class="comment">   * Use, basically, the method from `man cmsg` in Linux. */</span></div>
<div class="line"><a id="l00368" name="l00368"></a><span class="lineno">  368</span>  cmsghdr* <span class="keyword">const</span> recvmsg_hdr_cmsg_ptr = CMSG_FIRSTHDR(&amp;recvmsg_hdr);</div>
<div class="line"><a id="l00369" name="l00369"></a><span class="lineno">  369</span>  <span class="keywordflow">if</span> (recvmsg_hdr_cmsg_ptr)</div>
<div class="line"><a id="l00370" name="l00370"></a><span class="lineno">  370</span>  {</div>
<div class="line"><a id="l00371" name="l00371"></a><span class="lineno">  371</span>    <span class="comment">// There is some ancillary data.  It can only (validly according to our expected protocol) be one thing.</span></div>
<div class="line"><a id="l00372" name="l00372"></a><span class="lineno">  372</span>    <span class="keywordflow">if</span> ((recvmsg_hdr_cmsg_ptr-&gt;cmsg_level == SOL_SOCKET) &amp;&amp;</div>
<div class="line"><a id="l00373" name="l00373"></a><span class="lineno">  373</span>        (recvmsg_hdr_cmsg_ptr-&gt;cmsg_type == SCM_RIGHTS))</div>
<div class="line"><a id="l00374" name="l00374"></a><span class="lineno">  374</span>    {</div>
<div class="line"><a id="l00375" name="l00375"></a><span class="lineno">  375</span>      <span class="keyword">static_assert</span>(N_PAYLOAD_FDS == 1, <span class="stringliteral">&quot;Should be only dealing with one native handle with recvmsg() &quot;</span></div>
<div class="line"><a id="l00376" name="l00376"></a><span class="lineno">  376</span>                                        <span class="stringliteral">&quot;as of this writing.&quot;</span>);</div>
<div class="line"><a id="l00377" name="l00377"></a><span class="lineno">  377</span>      target_payload_hndl.m_native_handle</div>
<div class="line"><a id="l00378" name="l00378"></a><span class="lineno">  378</span>        = *(<span class="keyword">reinterpret_cast&lt;</span><span class="keyword">const </span><a class="code hl_typedef" href="structipc_1_1util_1_1Native__handle.html#a7194e8aaf9fc0109aad80222ae4ecb25">Native_handle::handle_t</a>*<span class="keyword">&gt;</span>(CMSG_DATA(recvmsg_hdr_cmsg_ptr)));</div>
<div class="line"><a id="l00379" name="l00379"></a><span class="lineno">  379</span>    }</div>
<div class="line"><a id="l00380" name="l00380"></a><span class="lineno">  380</span>    <span class="keywordflow">else</span></div>
<div class="line"><a id="l00381" name="l00381"></a><span class="lineno">  381</span>    {</div>
<div class="line"><a id="l00382" name="l00382"></a><span class="lineno">  382</span>      FLOW_LOG_WARNING(<span class="stringliteral">&quot;Connected local peer socket tried to read up to [&quot;</span> &lt;&lt; target_payload_blob.size() &lt;&lt; <span class="stringliteral">&quot;] bytes &quot;</span></div>
<div class="line"><a id="l00383" name="l00383"></a><span class="lineno">  383</span>                       <span class="stringliteral">&quot;at location @ [&quot;</span> &lt;&lt; target_payload_blob.data() &lt;&lt; <span class="stringliteral">&quot;] plus possibly a native handle; &quot;</span></div>
<div class="line"><a id="l00384" name="l00384"></a><span class="lineno">  384</span>                       <span class="stringliteral">&quot;and it returned it read [&quot;</span> &lt;&lt; n_rcvd_or_error &lt;&lt; <span class="stringliteral">&quot;] bytes successfully but also &quot;</span></div>
<div class="line"><a id="l00385" name="l00385"></a><span class="lineno">  385</span>                       <span class="stringliteral">&quot;unexpected ancillary data of csmg_level|cmsg_type &quot;</span></div>
<div class="line"><a id="l00386" name="l00386"></a><span class="lineno">  386</span>                       <span class="stringliteral">&quot;[&quot;</span> &lt;&lt; recvmsg_hdr_cmsg_ptr-&gt;cmsg_level &lt;&lt; <span class="charliteral">&#39;|&#39;</span> &lt;&lt; recvmsg_hdr_cmsg_ptr-&gt;cmsg_type &lt;&lt; <span class="stringliteral">&quot;].  &quot;</span></div>
<div class="line"><a id="l00387" name="l00387"></a><span class="lineno">  387</span>                       <span class="stringliteral">&quot;Acting as if nothing received + error.&quot;</span>);</div>
<div class="line"><a id="l00388" name="l00388"></a><span class="lineno">  388</span>      *err_code = <a class="code hl_enumvalue" href="namespaceipc_1_1transport_1_1error.html#adfef15ef4e76cc55d652fbd9c2797297a8c068cf7b73b09b5ed3fa3532de1747c">error::Code::S_LOW_LVL_UNEXPECTED_STREAM_PAYLOAD_BEYOND_HNDL</a>;</div>
<div class="line"><a id="l00389" name="l00389"></a><span class="lineno">  389</span>      <span class="keywordflow">return</span> 0; <span class="comment">// target_payload_hndl already set.</span></div>
<div class="line"><a id="l00390" name="l00390"></a><span class="lineno">  390</span>    }</div>
<div class="line"><a id="l00391" name="l00391"></a><span class="lineno">  391</span>    <span class="comment">// else</span></div>
<div class="line"><a id="l00392" name="l00392"></a><span class="lineno">  392</span>    <span class="keywordflow">if</span> (CMSG_NXTHDR(&amp;recvmsg_hdr, recvmsg_hdr_cmsg_ptr))</div>
<div class="line"><a id="l00393" name="l00393"></a><span class="lineno">  393</span>    {</div>
<div class="line"><a id="l00394" name="l00394"></a><span class="lineno">  394</span>      <span class="comment">/* This is rather strange: we didn&#39;t provide enough space for more ancillary data; yet there is somehow more,</span></div>
<div class="line"><a id="l00395" name="l00395"></a><span class="lineno">  395</span><span class="comment">       * even though we didn&#39;t detect MSG_CTRUNC earlier.  Well, whatever.  It&#39;s bad just like MSG_CTRUNC. */</span></div>
<div class="line"><a id="l00396" name="l00396"></a><span class="lineno">  396</span>      FLOW_LOG_WARNING(<span class="stringliteral">&quot;Connected local peer socket tried to read up to [&quot;</span> &lt;&lt; target_payload_blob.size() &lt;&lt; <span class="stringliteral">&quot;] bytes &quot;</span></div>
<div class="line"><a id="l00397" name="l00397"></a><span class="lineno">  397</span>                       <span class="stringliteral">&quot;at location @ [&quot;</span> &lt;&lt; target_payload_blob.data() &lt;&lt; <span class="stringliteral">&quot;] plus possibly a native handle; &quot;</span></div>
<div class="line"><a id="l00398" name="l00398"></a><span class="lineno">  398</span>                       <span class="stringliteral">&quot;and it returned it read [&quot;</span> &lt;&lt; n_rcvd_or_error &lt;&lt; <span class="stringliteral">&quot;] bytes and native handle &quot;</span></div>
<div class="line"><a id="l00399" name="l00399"></a><span class="lineno">  399</span>                       <span class="stringliteral">&quot;[&quot;</span> &lt;&lt; target_payload_hndl &lt;&lt; <span class="stringliteral">&quot;] but also more ancillary data; but we expect at most 1 native &quot;</span></div>
<div class="line"><a id="l00400" name="l00400"></a><span class="lineno">  400</span>                       <span class="stringliteral">&quot;handle.  Other side sent something strange.  Acting as if nothing received + error.&quot;</span>);</div>
<div class="line"><a id="l00401" name="l00401"></a><span class="lineno">  401</span>      target_payload_hndl = <a class="code hl_typedef" href="namespaceipc_1_1transport.html#a7ee4551983d9df16ec16a3139bac50e8">Native_handle</a>(); <span class="comment">// Undo the above (to match promised semantics on error).</span></div>
<div class="line"><a id="l00402" name="l00402"></a><span class="lineno">  402</span>      *err_code = <a class="code hl_enumvalue" href="namespaceipc_1_1transport_1_1error.html#adfef15ef4e76cc55d652fbd9c2797297a8c068cf7b73b09b5ed3fa3532de1747c">error::Code::S_LOW_LVL_UNEXPECTED_STREAM_PAYLOAD_BEYOND_HNDL</a>;</div>
<div class="line"><a id="l00403" name="l00403"></a><span class="lineno">  403</span>      <span class="keywordflow">return</span> 0;</div>
<div class="line"><a id="l00404" name="l00404"></a><span class="lineno">  404</span>    }</div>
<div class="line"><a id="l00405" name="l00405"></a><span class="lineno">  405</span>    <span class="comment">// else { No more ancillary data, as expected. }</span></div>
<div class="line"><a id="l00406" name="l00406"></a><span class="lineno">  406</span>  }</div>
<div class="line"><a id="l00407" name="l00407"></a><span class="lineno">  407</span>  <span class="comment">// else { No ancillary data, meaning no native handle; that&#39;s quite normal. }</span></div>
<div class="line"><a id="l00408" name="l00408"></a><span class="lineno">  408</span> </div>
<div class="line"><a id="l00409" name="l00409"></a><span class="lineno">  409</span>  FLOW_LOG_TRACE(<span class="stringliteral">&quot;recvmsg() reports receipt of possible native handle [&quot;</span> &lt;&lt; target_payload_hndl &lt;&lt; <span class="stringliteral">&quot;]; as well as &quot;</span></div>
<div class="line"><a id="l00410" name="l00410"></a><span class="lineno">  410</span>                 <span class="stringliteral">&quot;[&quot;</span> &lt;&lt; n_rcvd_or_error &lt;&lt; <span class="stringliteral">&quot;] of the blob&#39;s [&quot;</span> &lt;&lt; target_payload_blob.size() &lt;&lt; <span class="stringliteral">&quot;]-byte capacity.&quot;</span>);</div>
<div class="line"><a id="l00411" name="l00411"></a><span class="lineno">  411</span>  err_code-&gt;clear();</div>
<div class="line"><a id="l00412" name="l00412"></a><span class="lineno">  412</span>  <span class="keywordflow">return</span> n_rcvd_or_error;</div>
<div class="line"><a id="l00413" name="l00413"></a><span class="lineno">  413</span>} <span class="comment">// nb_read_some_with_native_handle()</span></div>
<div class="line"><a id="l00414" name="l00414"></a><span class="lineno">  414</span> </div>
<div class="line"><a id="l00415" name="l00415"></a><span class="lineno"><a class="line" href="namespaceipc_1_1transport_1_1asio__local__stream__socket.html#af0833f160dffd7f1c6921d27883a186b">  415</a></span><span class="keywordtype">void</span> <a class="code hl_function" href="namespaceipc_1_1transport_1_1asio__local__stream__socket.html#af0833f160dffd7f1c6921d27883a186b">release_native_peer_socket</a>(<a class="code hl_struct" href="structipc_1_1util_1_1Native__handle.html">Native_handle</a>&amp;&amp; peer_socket_native_or_null)</div>
<div class="line"><a id="l00416" name="l00416"></a><span class="lineno">  416</span>{</div>
<div class="line"><a id="l00417" name="l00417"></a><span class="lineno">  417</span>  <span class="keyword">using </span>flow::util::Task_engine;</div>
<div class="line"><a id="l00418" name="l00418"></a><span class="lineno">  418</span> </div>
<div class="line"><a id="l00419" name="l00419"></a><span class="lineno">  419</span>  <span class="comment">// As promised:</span></div>
<div class="line"><a id="l00420" name="l00420"></a><span class="lineno">  420</span>  <span class="keywordflow">if</span> (peer_socket_native_or_null.null())</div>
<div class="line"><a id="l00421" name="l00421"></a><span class="lineno">  421</span>  {</div>
<div class="line"><a id="l00422" name="l00422"></a><span class="lineno">  422</span>    <span class="keywordflow">return</span>;</div>
<div class="line"><a id="l00423" name="l00423"></a><span class="lineno">  423</span>  }</div>
<div class="line"><a id="l00424" name="l00424"></a><span class="lineno">  424</span>  <span class="comment">// else</span></div>
<div class="line"><a id="l00425" name="l00425"></a><span class="lineno">  425</span> </div>
<div class="line"><a id="l00426" name="l00426"></a><span class="lineno">  426</span>  <span class="comment">/* Purely for style reasons let&#39;s wrap it in a boost.asio `socket` and let its dtor</span></div>
<div class="line"><a id="l00427" name="l00427"></a><span class="lineno">  427</span><span class="comment">   * take care of it.  ::close() would have worked too, but I suppose this is less &quot;native&quot; and more</span></div>
<div class="line"><a id="l00428" name="l00428"></a><span class="lineno">  428</span><span class="comment">   * consistent. */</span></div>
<div class="line"><a id="l00429" name="l00429"></a><span class="lineno">  429</span>  Task_engine task_engine;</div>
<div class="line"><a id="l00430" name="l00430"></a><span class="lineno">  430</span>  [[maybe_unused]] <a class="code hl_typedef" href="namespaceipc_1_1transport_1_1asio__local__stream__socket.html#a1788f9dbd896bb71b3693f9ae25b40ae">Peer_socket</a> sock(task_engine, <a class="code hl_typedef" href="namespaceipc_1_1transport_1_1asio__local__stream__socket.html#a0ad6afc0bbf995a5b84528f96315f4a2">Protocol</a>(), peer_socket_native_or_null.m_native_handle);</div>
<div class="line"><a id="l00431" name="l00431"></a><span class="lineno">  431</span> </div>
<div class="line"><a id="l00432" name="l00432"></a><span class="lineno">  432</span>  peer_socket_native_or_null = <a class="code hl_typedef" href="namespaceipc_1_1transport.html#a7ee4551983d9df16ec16a3139bac50e8">Native_handle</a>(); <span class="comment">// As promised nullify it.</span></div>
<div class="line"><a id="l00433" name="l00433"></a><span class="lineno">  433</span> </div>
<div class="line"><a id="l00434" name="l00434"></a><span class="lineno">  434</span>  <span class="comment">// Now destroy `sock`, then destroy task_engine.</span></div>
<div class="line"><a id="l00435" name="l00435"></a><span class="lineno">  435</span>} <span class="comment">// release_native_peer_socket()</span></div>
<div class="line"><a id="l00436" name="l00436"></a><span class="lineno">  436</span> </div>
<div class="line"><a id="l00437" name="l00437"></a><span class="lineno">  437</span><span class="comment">// Opt_peer_process_credentials implementations.</span></div>
<div class="line"><a id="l00438" name="l00438"></a><span class="lineno">  438</span> </div>
<div class="line"><a id="l00439" name="l00439"></a><span class="lineno">  439</span><a class="code hl_function" href="classipc_1_1transport_1_1asio__local__stream__socket_1_1Opt__peer__process__credentials.html#a09c70548774b3e063500a04d4f72d803">Opt_peer_process_credentials::Opt_peer_process_credentials</a>() = <span class="keywordflow">default</span>;</div>
<div class="line"><a id="l00440" name="l00440"></a><span class="lineno">  440</span><a class="code hl_function" href="classipc_1_1transport_1_1asio__local__stream__socket_1_1Opt__peer__process__credentials.html#a09c70548774b3e063500a04d4f72d803">Opt_peer_process_credentials::Opt_peer_process_credentials</a>(<span class="keyword">const</span> Opt_peer_process_credentials&amp;) = <span class="keywordflow">default</span>;</div>
<div class="line"><a id="l00441" name="l00441"></a><span class="lineno">  441</span>Opt_peer_process_credentials&amp; <a class="code hl_function" href="classipc_1_1transport_1_1asio__local__stream__socket_1_1Opt__peer__process__credentials.html#a0e8dd6f2ba88ceef69391578a6dcf45c">Opt_peer_process_credentials::operator=</a>(<span class="keyword">const</span> Opt_peer_process_credentials&amp;) = <span class="keywordflow">default</span>;</div>
<div class="line"><a id="l00442" name="l00442"></a><span class="lineno">  442</span> </div>
<div class="line"><a id="l00443" name="l00443"></a><span class="lineno">  443</span>} <span class="comment">// namespace ipc::transport::asio_local_stream_socket</span></div>
<div class="ttc" id="aasio__local__stream__socket_8hpp_html"><div class="ttname"><a href="asio__local__stream__socket_8hpp.html">asio_local_stream_socket.hpp</a></div></div>
<div class="ttc" id="aclassipc_1_1transport_1_1asio__local__stream__socket_1_1Opt__peer__process__credentials_html_a09c70548774b3e063500a04d4f72d803"><div class="ttname"><a href="classipc_1_1transport_1_1asio__local__stream__socket_1_1Opt__peer__process__credentials.html#a09c70548774b3e063500a04d4f72d803">ipc::transport::asio_local_stream_socket::Opt_peer_process_credentials::Opt_peer_process_credentials</a></div><div class="ttdeci">Opt_peer_process_credentials()</div><div class="ttdoc">Default ctor: each value is initialized to zero or equivalent.</div></div>
<div class="ttc" id="aclassipc_1_1transport_1_1asio__local__stream__socket_1_1Opt__peer__process__credentials_html_a0e8dd6f2ba88ceef69391578a6dcf45c"><div class="ttname"><a href="classipc_1_1transport_1_1asio__local__stream__socket_1_1Opt__peer__process__credentials.html#a0e8dd6f2ba88ceef69391578a6dcf45c">ipc::transport::asio_local_stream_socket::Opt_peer_process_credentials::operator=</a></div><div class="ttdeci">Opt_peer_process_credentials &amp; operator=(const Opt_peer_process_credentials &amp;src)</div><div class="ttdoc">Boring copy assignment.</div></div>
<div class="ttc" id="aipc__core_2src_2ipc_2transport_2error_8hpp_html"><div class="ttname"><a href="ipc__core_2src_2ipc_2transport_2error_8hpp.html">error.hpp</a></div></div>
<div class="ttc" id="anamespaceipc_1_1transport_1_1asio__local__stream__socket_html"><div class="ttname"><a href="namespaceipc_1_1transport_1_1asio__local__stream__socket.html">ipc::transport::asio_local_stream_socket</a></div><div class="ttdoc">Additional (versus boost.asio) APIs for advanced work with local stream (Unix domain) sockets includi...</div><div class="ttdef"><b>Definition:</b> <a href="asio__local__stream__socket_8cpp_source.html#l00031">asio_local_stream_socket.cpp:32</a></div></div>
<div class="ttc" id="anamespaceipc_1_1transport_1_1asio__local__stream__socket_html_a0ad6afc0bbf995a5b84528f96315f4a2"><div class="ttname"><a href="namespaceipc_1_1transport_1_1asio__local__stream__socket.html#a0ad6afc0bbf995a5b84528f96315f4a2">ipc::transport::asio_local_stream_socket::Protocol</a></div><div class="ttdeci">local_ns::stream_protocol Protocol</div><div class="ttdoc">Short-hand for boost.asio Unix domain stream-socket protocol.</div><div class="ttdef"><b>Definition:</b> <a href="asio__local__stream__socket__fwd_8hpp_source.html#l00108">asio_local_stream_socket_fwd.hpp:108</a></div></div>
<div class="ttc" id="anamespaceipc_1_1transport_1_1asio__local__stream__socket_html_a1022dfd42e9a0d6eab8384b0352decb0"><div class="ttname"><a href="namespaceipc_1_1transport_1_1asio__local__stream__socket.html#a1022dfd42e9a0d6eab8384b0352decb0">ipc::transport::asio_local_stream_socket::nb_write_some_with_native_handle</a></div><div class="ttdeci">size_t nb_write_some_with_native_handle(flow::log::Logger *logger_ptr, Peer_socket *peer_socket_ptr, Native_handle payload_hndl, const util::Blob_const &amp;payload_blob, Error_code *err_code)</div><div class="ttdoc">boost.asio extension similar to peer_socket-&gt;non_blocking(true); auto n = peer_socket-&gt;write_some(pay...</div><div class="ttdef"><b>Definition:</b> <a href="asio__local__stream__socket_8cpp_source.html#l00036">asio_local_stream_socket.cpp:36</a></div></div>
<div class="ttc" id="anamespaceipc_1_1transport_1_1asio__local__stream__socket_html_a1788f9dbd896bb71b3693f9ae25b40ae"><div class="ttname"><a href="namespaceipc_1_1transport_1_1asio__local__stream__socket.html#a1788f9dbd896bb71b3693f9ae25b40ae">ipc::transport::asio_local_stream_socket::Peer_socket</a></div><div class="ttdeci">Protocol::socket Peer_socket</div><div class="ttdoc">Short-hand for boost.asio Unix domain peer stream-socket (usually-connected-or-empty guy).</div><div class="ttdef"><b>Definition:</b> <a href="asio__local__stream__socket__fwd_8hpp_source.html#l00114">asio_local_stream_socket_fwd.hpp:114</a></div></div>
<div class="ttc" id="anamespaceipc_1_1transport_1_1asio__local__stream__socket_html_a9ae82b2a234b218704c62fb616d6fcc5"><div class="ttname"><a href="namespaceipc_1_1transport_1_1asio__local__stream__socket.html#a9ae82b2a234b218704c62fb616d6fcc5">ipc::transport::asio_local_stream_socket::nb_read_some_with_native_handle</a></div><div class="ttdeci">size_t nb_read_some_with_native_handle(flow::log::Logger *logger_ptr, Peer_socket *peer_socket_ptr, Native_handle *target_payload_hndl_ptr, const util::Blob_mutable &amp;target_payload_blob, Error_code *err_code, int message_flags)</div><div class="ttdoc">boost.asio extension similar to peer_socket-&gt;non_blocking(true); auto n = peer_socket-&gt;read_some(targ...</div><div class="ttdef"><b>Definition:</b> <a href="asio__local__stream__socket_8cpp_source.html#l00201">asio_local_stream_socket.cpp:201</a></div></div>
<div class="ttc" id="anamespaceipc_1_1transport_1_1asio__local__stream__socket_html_af0833f160dffd7f1c6921d27883a186b"><div class="ttname"><a href="namespaceipc_1_1transport_1_1asio__local__stream__socket.html#af0833f160dffd7f1c6921d27883a186b">ipc::transport::asio_local_stream_socket::release_native_peer_socket</a></div><div class="ttdeci">void release_native_peer_socket(Native_handle &amp;&amp;peer_socket_native_or_null)</div><div class="ttdoc">Little utility that returns the raw Native_handle suitable for Peer_socket to the OS.</div><div class="ttdef"><b>Definition:</b> <a href="asio__local__stream__socket_8cpp_source.html#l00415">asio_local_stream_socket.cpp:415</a></div></div>
<div class="ttc" id="anamespaceipc_1_1transport_1_1error_html_adfef15ef4e76cc55d652fbd9c2797297a8c068cf7b73b09b5ed3fa3532de1747c"><div class="ttname"><a href="namespaceipc_1_1transport_1_1error.html#adfef15ef4e76cc55d652fbd9c2797297a8c068cf7b73b09b5ed3fa3532de1747c">ipc::transport::error::Code::S_LOW_LVL_UNEXPECTED_STREAM_PAYLOAD_BEYOND_HNDL</a></div><div class="ttdeci">@ S_LOW_LVL_UNEXPECTED_STREAM_PAYLOAD_BEYOND_HNDL</div><div class="ttdoc">Unable to receive incoming traffic: message contains more than: 1 blob plus 0-1 native handles.</div></div>
<div class="ttc" id="anamespaceipc_1_1transport_html_a7ee4551983d9df16ec16a3139bac50e8"><div class="ttname"><a href="namespaceipc_1_1transport.html#a7ee4551983d9df16ec16a3139bac50e8">ipc::transport::Native_handle</a></div><div class="ttdeci">util::Native_handle Native_handle</div><div class="ttdoc">Convenience alias for the commonly used type util::Native_handle.</div><div class="ttdef"><b>Definition:</b> <a href="transport__fwd_8hpp_source.html#l00081">transport_fwd.hpp:81</a></div></div>
<div class="ttc" id="anamespaceipc_1_1util_html_a6cb62ae434900f3a8915b33ec5d61a96"><div class="ttname"><a href="namespaceipc_1_1util.html#a6cb62ae434900f3a8915b33ec5d61a96">ipc::util::Blob_mutable</a></div><div class="ttdeci">boost::asio::mutable_buffer Blob_mutable</div><div class="ttdoc">Short-hand for an mutable blob somewhere in memory, stored as exactly a void* and a size_t.</div><div class="ttdef"><b>Definition:</b> <a href="util__fwd_8hpp_source.html#l00140">util_fwd.hpp:140</a></div></div>
<div class="ttc" id="anamespaceipc_1_1util_html_ae0be7edba7e30ffa3f8b742af621f2ab"><div class="ttname"><a href="namespaceipc_1_1util.html#ae0be7edba7e30ffa3f8b742af621f2ab">ipc::util::Blob_const</a></div><div class="ttdeci">boost::asio::const_buffer Blob_const</div><div class="ttdoc">Short-hand for an immutable blob somewhere in memory, stored as exactly a void const * and a size_t.</div><div class="ttdef"><b>Definition:</b> <a href="util__fwd_8hpp_source.html#l00134">util_fwd.hpp:134</a></div></div>
<div class="ttc" id="anamespaceipc_html_aa3192e586cc45d3e7c22463bf2760f89"><div class="ttname"><a href="namespaceipc.html#aa3192e586cc45d3e7c22463bf2760f89">ipc::Error_code</a></div><div class="ttdeci">flow::Error_code Error_code</div><div class="ttdoc">Short-hand for flow::Error_code which is very common.</div><div class="ttdef"><b>Definition:</b> <a href="common_8hpp_source.html#l00298">common.hpp:298</a></div></div>
<div class="ttc" id="astructipc_1_1util_1_1Native__handle_html"><div class="ttname"><a href="structipc_1_1util_1_1Native__handle.html">ipc::util::Native_handle</a></div><div class="ttdoc">A monolayer-thin wrapper around a native handle, a/k/a descriptor a/k/a FD.</div><div class="ttdef"><b>Definition:</b> <a href="native__handle_8hpp_source.html#l00062">native_handle.hpp:63</a></div></div>
<div class="ttc" id="astructipc_1_1util_1_1Native__handle_html_a7194e8aaf9fc0109aad80222ae4ecb25"><div class="ttname"><a href="structipc_1_1util_1_1Native__handle.html#a7194e8aaf9fc0109aad80222ae4ecb25">ipc::util::Native_handle::handle_t</a></div><div class="ttdeci">int handle_t</div><div class="ttdoc">The native handle type. Much logic relies on this type being light-weight (fast to copy).</div><div class="ttdef"><b>Definition:</b> <a href="native__handle_8hpp_source.html#l00067">native_handle.hpp:67</a></div></div>
<div class="ttc" id="astructipc_1_1util_1_1Native__handle_html_ab2f496740139c5752a25a30cf3325d86"><div class="ttname"><a href="structipc_1_1util_1_1Native__handle.html#ab2f496740139c5752a25a30cf3325d86">ipc::util::Native_handle::m_native_handle</a></div><div class="ttdeci">handle_t m_native_handle</div><div class="ttdoc">The native handle (possibly equal to S_NULL_HANDLE), the exact payload of this Native_handle.</div><div class="ttdef"><b>Definition:</b> <a href="native__handle_8hpp_source.html#l00085">native_handle.hpp:85</a></div></div>
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